Plugin and error
- Go course
- Advanced
- Lesson 23/68
- 4 min
Learn to handle plugin loading errors.
Plugin errors
Errors come from three places: Open (missing file, version mismatch), Lookup (missing symbol) and the type assertion (wrong type). The single-value form of a type assertion panics; the two-value form is safe:
f, ok := sym.(func(string) string)
if !ok {
return errors.New("Selam beklenen türde değil")
}Wrapping errors
Wrap errors with context to see which plugin and which step failed:
p, err := plugin.Open(yol)
if err != nil {
return fmt.Errorf("plugin %s açılamadı: %w", yol, err)
}%w keeps the original error, which can still be queried with errors.Is.
Practice Write a safe assertion
Declare var sym any = 42. Assert with f, ok := sym.(func() string); if ok is false print fmt.Println("tür uyumsuz").
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func main() {
var sym any = 42
f, ok := sym.(func() string)
if !ok {
fmt.Println("tür uyumsuz")
return
}
fmt.Println(f())
}Expected output
tür uyumsuz
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>f := sym.(func())</code> do if the assertion fails?
- It returns false
- It fails to compile
- It panics Correct answer
- f becomes nil
Explanation: A single-value type assertion panics on mismatch; the ", ok" form gives ok=false instead.
2 Safe assertion
f, ____ := sym.(func() string)
if !ok { return }f, ok := sym.(func() string)
if !ok { return }Explanation: In a two-value type assertion the second value is a bool reporting success.
3 Error source
| Term | Meaning |
|---|---|
Missing file |
plugin.Open |
Missing symbol |
Lookup |
Wrong type |
Type assertion |
Adding context |
fmt.Errorf and %w |